Practically nothing is known about longevity in _T. ornata_ or in
other species of _Terrapene_ although the several plausible records of
ages of 80 to more than 100 years for _T. carolina_ (Oliver,
1955:295-6) would indicate that box turtles, as a group, are
long-lived. There is no known way to determine accurately the age of
an adult turtle after it has stopped growing. It was possible
occasionally to determine ages of 20 to 30 years with fair accuracy by
counting all growth-rings (including those crowded into the
interabdominal seam) of specimens having unworn shells. Without the
presence of newly formed epidermis as a landmark, however, it was
never certain how many years had passed since the last ring was
formed.
[Illustration: FIG. 13. The relationship of sexual maturity to
size in 164 specimens (94 females and 70 males) of _Terrapene
o. ornata_, expressed as the percentage of mature individuals
in each of five groups arranged according to plastral length.
Sexual maturity was determined by examination of gonads. Solid
bars are for males and open bars for females. The bar for males
in the largest group is based on assumption since no males in
the sample were so long as 130 mm. Males mature at a smaller
size and lesser age (see also Figs. 9 and 10) than females.
Plastral lengths of the smallest sexually mature male and
female in the sample were, respectively, 99 and 107 mm.]
Mattox (1936) studied annual rings in the long bones of painted
turtles (_Chrysemys picta_) and found fewer rings in younger than in
older individuals but, beyond this, reached no important conclusion.
In the present study, thin sections were ground from the humeri and
femurs of box turtles of various ages and sizes; the results of this
investigation were negative. Distinct rings were present in the
compact bony tissue but it appeared that, after the first year or two,
the rings were destroyed by encroachment of the marrow cavity at about
the same rate at which they were formed peripherally.
The only methods that I know of to determine successfully the
longevity of long-lived reptiles would be to keep individuals under
observation for long periods of time or to study populations of marked
individuals. Both methods have the obvious disadvantage of requiring
somewhat more than a human lifetime to carry them to completion.
Restudy, after one or more decades, of the populations of turtles
marked by Fitch and myself may provide valuable data on the average
and maximum age reached by _T. ornata_.
Ornate box turtles probably live at least twice as long as the total
period of growing years. An estimated longevity of 50 years would seem
to agree with present scant information on age. Considering
environmental hazards, it would be unusual for an individual to
survive as long as 100 years in the wild.